1. Field of the Invention
The present invention relates to the art of monocrystalline body formation utilizing melts, e.g. the well-known Czochralski, Bridgeman or Kyropoulos techniques. In the Czochralski technique the monocrystalline body is formed by pulling a crystal from a melt contained within a crucible. Insulating material, specifically zirconia, is generally placed around the crucible.
The present invention pertains to a new insulating material which is an efficient absorber of near infrared radiation emitted by the melt at the elevated temperatures of boule formation. Dysprosium-containing compounds and specifically dysprosium oxide alone or combined with other refractories such as zirconium, hafnium and thorium oxides is disclosed.
2. Description of the Prior Art
The use of insulation in crystal growth chambers/furnaces for Czochralski technique monocrystalline formation is well known and zironia has been used for this purpose. See for example, U.S. Pat. No. 4,199,396.
The presence of temperature gradients within melts utilized in crystal formation also has long been recognized as detrimental to optimal crystal formation. Various methods of reducing such temperature gradients have been developed. See for example, U.S. Pat. Nos. 2,956,863; 3,240,568 and 4,032,390.
In accordance with the present invention, it has been discovered that the radial temperature gradients of crystal-forming melts within Czochralski crystal growth apparatuses, that is, single crystal growth furnaces, can be reduced by utilizing the insulating material of the invention with attendant improvement in crystal quality. It has also been discovered that the power of the RF coil used to form and maintain the melt is reduced where the insulating matter selected is an efficient absorber of the near infrared radiant energy emitted by the crucible and melt at the temperature levels of crystal pulling.